polymer synthesis chem 421 semiconductor manufacturing

Polymer SynthesisCHEM 421Semiconductor Manufacturing

Polymer SynthesisCHEM 421

Photolithographic Process

J. Phys. Org. Chem. 2000, 13, 767.

Coat

Exposure

Develop

Strip

Etch

Photoresist

Substrate

Maskh

PositiveNegative


Important Properties of a Photoresist

• Resist Thickness (etch resistance)Resist Thickness (etch resistance)

• Solubility for deposition/developmentSolubility for deposition/development

• WettabilityWettability

• Lithographic performanceLithographic performance

–Sensitivity, contrastSensitivity, contrast

• TransparencyTransparency(more important for 193 nm and beyond)(more important for 193 nm and beyond)


Optics of Imaging

R = resolution = smallest feature sizeR / NA

• is the wavelength of light• NA is the numerical aperture (a function of the optics)

Wavelength Wavelength 365 nm 248 nm 193 nm 157 nm

NotationNotation i-line DUV 193 nm 157 nm

mercury KrF ArF F2 excimer Source Source lamp excimer excimer laser laser laser

Feature Size Feature Size 365+ nm 500 - 100 nm 130 - 70 nm* 90 - 45 nm*


G- and I-line Resists

• Novolac resinNovolac resin– Base-soluble positive resist (TMAH)Base-soluble positive resist (TMAH)– Variety of structures and MW’sVariety of structures and MW’s

• Diazonapthaquinone (DNQ)Diazonapthaquinone (DNQ)– Photoactive compound (Wolfe Rearrangement)Photoactive compound (Wolfe Rearrangement)– Inhibits base-dissolution of novolacInhibits base-dissolution of novolac

OH

CH3

OH

CH3

CH2

O

N2

R

O

R R

C

O

H2O

R

CO2H

h

-N2

Polymer SynthesisCHEM 421“Transitions” in Optical Lithography

365 nm365 nm

248 nm248 nm


Chemical Amplification

• DUV exposure generates catalytic DUV exposure generates catalytic amount of acid from a photoacid amount of acid from a photoacid generator (PAG)generator (PAG)

• 1-2 min PEB to trigger 1-2 min PEB to trigger deprotectiondeprotection

• Catalytic chain length is extremely Catalytic chain length is extremely longlong

– About 500 - 1000 About 500 - 1000 carbonate cleavages per carbonate cleavages per protonproton

H+

CH CH2

O

O

O

H+

J. Phys. Org. Chem. 2000, 13, 767.Acc. Chem Res. 1994, 27, 150.

CH CH2

O

O

O

CH CH2

O

OH

O

CH CH2

OH

C

O

OH

H+


Challenges with Chemical Amplification

• What if trace amounts of base (NMP solvent) What if trace amounts of base (NMP solvent) was found in the air in a FAB?was found in the air in a FAB?

Levinson, Harry J. Principles of Lithography. SPIE Press, 2001.

• Catalyst Catalyst susceptible to susceptible to poisoning by poisoning by atmospheric atmospheric basesbases


Model for Constructing a Chemically Amplified Resist


Etch Barrier

Backbone

Protecting Group

Acidic Group

CH CH2 CH CH2

OOH

O

O


Low- and High-Activation Energy Chemically Amplified Resists

CH CH2

O

O

O

CH CH2

OH

• Copolymer of hydroxy styrene and t-BOC protected hydroxy styrene• Good hydrophilic/hydrophobic balance• IBM’s Apex Resist• Low activation energy, very reactive• PAB below Tg

CH CH2

C

CH CH2

OH

O

O

• IBM’s ESCAP Resist• High activation energy, lower reactivity• Allows for high T bake• PAB above Tg

• removes stress• removes residual solvent• higher density films• Low diffusion of PAG


365 nm365 nm

248 nm248 nm

193 nm193 nm

Polymer SynthesisCHEM 421Absorption of Resins

190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350

1.8

1.5

1.1

0.8

0.5

0.3

0.1

AbsorptionCoefficient(micron-1)

Wavelength (nm)

Poly(p-hydroxy styrene)

Polyacrylate

Optimal range

Polymer SynthesisCHEM 421Design Criteria for 193 nm Resists

• Optical transparency

• Hydrophilicity

• High Tg (130-170 °C)

• Good etch resistance

• Easily blocked hydroxyl group


Photoresists for 193 nm Lithography

CH2 C

CH3

CH2 C

CH3

CH2 C

CH3

O

OCH3

O

OH

O

O

C(CH3)3

CH2 C

CH3

CH2 C

CH3

CH2 C

CH3

O

OCH3

O

OH

O

OH

PAG

• Extremely transparent at 193 nm

• Tunable composition

• Property diversity

• Good hydrophilicity

• High activation energy

cleavable group

• Easily synthesized

• But poor etch resistance…



CH2 C

CH3

CH2 C

CH3

CH2 C

CH3

O

O

O

OH

O

O

O

Dry etch resistance &transparency

Cleavablegroup

Hydrophilicity



AT&T / Lucent / Agere

O

O

OO O

+ AIBN

THF

O

O

OO O


365 nm365 nm

248 nm248 nm

193 nm193 nm

157 nm157 nm

Absorptionat 157 nm??!!


PolymerPolymer

Absorbtion Absorbtion Coefficient Coefficient

(157 nm)(157 nm)

Thickness (nm)Thickness (nm)

(OD = 0.4)(OD = 0.4)

Poly(hydrosilsesquioxane)Poly(hydrosilsesquioxane) 0.060.06 66676667

Poly(tetrafluoroethylene)Poly(tetrafluoroethylene) 0.700.70 571571

Poly(tetrafluoroethylene-co-Poly(tetrafluoroethylene-co-ethylene) (30% TFE)ethylene) (30% TFE) 1.341.34 298298

Poly(dimethylsiloxane)Poly(dimethylsiloxane) 1.611.61 248248

Poly(vinyl alcohol)Poly(vinyl alcohol) 4.164.16 9696

Poly(methyl methacrylate)Poly(methyl methacrylate) 5.695.69 7070

Poly(norbornene)Poly(norbornene) 6.106.10 6666

PolystyrenePolystyrene 6.206.20 6464

Poly(p-hydroxystyrene)Poly(p-hydroxystyrene) 6.256.25 6464

Poly(p-chlorostyrene)Poly(p-chlorostyrene) 10.1510.15 3939

R. R. Kunz et.al. J. Vac. Sci. Technol. B 17(6), Nov/Dec 1999

Polymeric Materials Outlook for 157 nm Resist Design


Emerging 157 nm Resist Platforms

CF2CF2

A. E. Feiring and J. Feldman,DuPont WO 00/67072.

SO2

OHCF3

CF3

H. Ito, G. Walraff, et. al. IBM

CH2 C

C

OCH3

O

CF3

G. Willson, UT

O

O CF3

OHF3C

x y

G. Willson, UT

R. Dammel, Clariant

CH2 CH CH2

CH

O

O

O

O

CF3F3C

F3C CF3

OH

nm

O

C. Ober, Cornell

O.D. @ 157 nm1.4 micron-1

O.D. @ 157 nm3.1 micron-1

O.D. @ 157 nm2.7 micron-1 O.D. @ 157 nm

2.8 micron-1O.D. @ 157 nm

2.5 micron-1


Poly(TFE-co-NB-co-EVE)

•Lowers Absorbance

•Increases CO2 Solubility

•Increases Etch Resistance

•Increases Tg

•Provides Contrast

•Lowers Absorbance

•Increases CO2 Solubility

EVE is EVE is EEster ster VVinyl inyl EEtherther

CF2CF2 CF2 CF

OCF2 CF

CF3

OCF2

CF2

O

OMe


Poly(TFE-co-NB-co-EVE)

TFETFE(mol %)(mol %)

NBNB(mol %)(mol %)

FGFG(mol %)(mol %)

TTgg

((°°C)C)Mn /Mn /

MWDMWDLiq. COLiq. CO22

Sol.Sol.Abs.Abs.

@ 157 nm@ 157 nm

5050

3838

5050

5959

00

33

125125

126126

????

3300 /3300 /1.471.47

Insol.Insol.

Insol.Insol.

1.41.4

1.381.38

4040 5555 55 1151153600 /3600 /1.321.32 Insol.Insol. 1.291.29

4141 5252 77 92923500 /3500 /1.421.42 Insol.Insol. To be To be

determineddetermined

CF2CF2 CF2 CF

OCF2 CF

CF3

OCF2

CF2

O

OMe


157/193 nm PhotoresistsTeflon® AF as Backbone Material

• Due to its amorphous structure and rigid backbone, Teflon® AF has unique Due to its amorphous structure and rigid backbone, Teflon® AF has unique properties that are desirable in a photoresist backboneproperties that are desirable in a photoresist backbone

Advantages Challenges

• very low absorbance • cost of PDD monomer

• rigid structure (good etch resistance)

• need functional monomer without significantly increasing absorbance

• forms smooth films

• broad range of Tgs available

Tetrafluoroethylene(TFE)

2,2-Bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole

(PDD)

CF2 CF2 + CF2 CF2 / CF CF

O O

F3C CF3

i

CF CF

O O

F3C CF3

Teflon® AFTeflon® AF


157/193 nm PhotoresistsAbsorbance at 157 nm and 193 nm

• Values for Teflon® AF and Values for Teflon® AF and the CO2 synthesized the CO2 synthesized copolymer are very close copolymer are very close and well below 1 and well below 1 mm-1 -1 at at 157 nm 157 nm

• Values at 193 nm are Values at 193 nm are slightly different but both slightly different but both extremely lowextremely low

Sample 157.6 (nm)

193 (nm)

Teflon® AF 0.154 0.004

CO2 Synthesized Copolymer

0.153 0.019

Absorbance [Absorbance [mmOptical Density

0

0.5

1

1.5

2

2.5

145 155 165 175 185 195

wavelength (nm)

(m

-1)

Teflon AF CO2 Synthesized Copolymer

T


157/193 nm PhotoresistsTeflon® AF as Backbone Material

Protected Functional Monomer

Acidic Group

CF2 CF2 CF CF

OO

CF3F3C

CF2 CF2 CF CF

OO

CF3F3C

PAG

• In order for a Teflon® AF In order for a Teflon® AF derivative to serve as a derivative to serve as a photoresist, a functionalized photoresist, a functionalized monomer that can be monomer that can be cleaved by an acid must be cleaved by an acid must be incorporated into the incorporated into the backbonebackbone

• After cleaving with a photo After cleaving with a photo acid generator (PAG) the acid generator (PAG) the functional monomer will functional monomer will exhibit different solubility exhibit different solubility properties from unexposed properties from unexposed regionsregions


157/193 nm Photoresists EVE/PDD/TFE Plackett-Burman Experiment Scheme

• Chose to explore Ester Vinyl Ether (EVE) Chose to explore Ester Vinyl Ether (EVE) as a prototype for potential EVE derived as a prototype for potential EVE derived functional monomersfunctional monomers

• Conducted a Plackett-Burman Conducted a Plackett-Burman experimental scheme varying five experimental scheme varying five parameters (composition, initiator parameters (composition, initiator concentration, temperature, pressure and concentration, temperature, pressure and reaction time) to study the reaction of EVE reaction time) to study the reaction of EVE with PDD and TFEwith PDD and TFE

Exp. # EVE/PDD/TFE (mol %)

Initiator (mol %)

Temp (oC) Pressure (psi)

Rxn Time (hr)

1 7/73/20 1 15 3500 4

2 25/55/20 0.2 35 3500 4

3 25/55/20 0.2 15 3500 0.5

4 25/55/20 1 15 1500 4

5 7/73/20 1 35 3500 0.5

6 7/73/20 0.2 35 1500 4

7 25/55/20 1 35 1500 0.5

8 7/73/20 0.2 15 1500 0.5

CF2 CF2 CF CF

OO

CF3F3C

F2C

O

CF

CF3

O CF2 CF2

O

OCH3

CF CF

poly(TFE-co-PDD-co-EVE)


157/193 nm Photoresists EVE/TFE/PDD - Absorbance

• Absorbance values at 157 nm increase with increasing EVE Absorbance values at 157 nm increase with increasing EVE content but still remain well below 1 content but still remain well below 1 mm

• Values at 193 nm are very low and vary only slightlyValues at 193 nm are very low and vary only slightly

Sample Composition(mol %)

157.6(nm)

193(nm)

REH-004 7/73/20 EVE/PDD/TFE (Charged) 0.128 0.013

REH-013 12/59/29EVE/PDD/TFE 0.252 0.011

REH-005 18/54/28EVE/PDD/TFE 0.574 0.017

VASE® Absorbance [VASE® Absorbance [mmMeasurementsMeasurements


Bilayer Resist Processes



Top-Surface Imaging



Comparisons

Spin coating

Expose

Develop

1st Spin coating

2nd Spin coating

Expose

Develop

O2-RIE

Spin coating

NegativeExposure

Single LayerResist

Top-SurfaceImaged Resist

Bi-LayerResist

O2-RIE

Silylate


365 nm365 nm

248 nm248 nm

193 nm193 nm

157 nm157 nm

E-beamE-beam

X-rayX-ray

EUVEUV

?


“Advances in Patterning Materials for 193 nm Immersion Lithography”

Chem. Rev. 2010, 110, 321–360

“Organic imaging materials: a view of the future”

J. Phys. Org. Chem. 2000, 13, 767

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